PROJECT SUMMARY Tumors are initiated and maintained by a stem cell-like population. However, our bodies have a powerful immune surveillance system to clear out cancerous cells as they emerge. Whether tumor-initiating stem cells (tSCs) are programmed to resist anti-tumor immunity and/or how they overcome the barrier of immune surveillance remains poorly understood. Previously, we have designed a novel skin squamous cell carcinoma (SCC) mouse model that can be effectively targeted by adoptive T cell transfer (ACT) based immunotherapy, in which the CD8+ cytotoxic T cells are engineered to recognize a tumor-specific neoantigen, then are activated and reintroduced to the body to attack tumor. In this model, we have successfully demonstrated that a subset of tSCs are surprisingly refractory to the antigen-specific T cell treatment, and cause the tumor to relapse. Since tumor relapse is a major clinical obstacle for patients receiving ACT, understanding the factors that sustain immune evasive SCs is paramount for limiting relapse in ACT. Therefore, with my strong background in immunology, I'm especially interested in how these highly plastic stem cells receive special cues to develop resistance or become evasive to the anti-tumor immunity. Our preliminary data shows that tSCs must sequentially undergo three stages involving distinct immune evasive. Specifically, the tSCs must firstly, endure massive T cell attack during the initial primary tumor clearance stage; then become quiescent while still evade immune detection to maintain a long period of dormancy; finally, exclude the infiltrating T cells in order to exit dormancy and generate relapsed tumors. We hypothesize that specific signaling cue activates different cohort of genes in stem cells during each of the three stage of tumor relapse and dictates stage-specific immune evasive program. Driven by this hypothesis and built on strong preliminary data, I found that Wnt/?- Catenin signaling, an essential pathway for stem cell functions is critical in each of these three stages of tumor relapse. Now I designed comprehensive research aims to systematically interrogate the stem cells and sought to identify Wnt-regulated genes and their mechanisms promoting each stage of tumor relapse from ACT treatment. My plan for the remainder of my postdoctoral training is to acquire additional skills and develop research tools to tackle this fascinating question, and to open a door for establishing independence in academia. My long-term research objective is to identify new druggable targets that could potentially lead to next generation of immunotherapy that is designed to eliminate the tSCs. I expect the originality of my approaches and identification of novel Wnt targets regulating tumor immune evasion will allow me to build a solid foundation for a future independent research program. More importantly, I expect that the data generated from my related but independent aims will unveil new tumor-intrinsic targets that will not only expand our knowledge of tumor-immune interactions, but also pave the way to develop new strategies to enhance the efficacy of current ACT treatments and surmount this major clinical obstacle.